Up to 700,000 likely to attend ceremonies, less than half 2009's 2 million

Today's oath follows yesterday's official swearing-in

WASHINGTON - Facing a divided political system, economic troubles at home and continued unrest overseas, President Obama urged

Americans to work together to "face the realities of our time."

"This generation of Americans has been tested by crises that steeled our resolve and proved our resilience. A decade of war is now ending. An economic recovery has begun. America's possibilities are limitless, for we possess all the qualities that this world without boundaries demands: youth and drive; diversity and openness; an endless capacity for risk and a gift for reinvention. My fellow Americans, we are made for this moment, and we will seize it - so long as we seize it together."

Obama's 18-minute speech touched on the tragedy in Newtown, education, jobs and the swelling federal budget deficit, but it acknowledged polarizing politics that have divided much of the nation. "Being true to our founding documents does not require us to agree on every contour of life; it does not mean we will all define liberty in exactly the same way, or follow the same precise path to happiness. Progress does not compel us to settle centuries-long debates about the role of government for all time - but it does require us to act in our time,'' Obama said.

"For now decisions are upon us, and we cannot afford delay. We cannot mistake absolutism for principle, or substitute spectacle for politics, or treat name-calling as reasoned debate. We must act, knowing that our work will be imperfect."

Earlier, Obama declared in tweets that "our work begins today" and vowed to "finish what we started" before arriving at the Capitol.

Obama adviser David Axelrod told CBS' This Morning that the speech was designed to focus on "values and principles, not so much about programs and prescriptions."

Thousands began gathering in the dark, chilly predawn hours to see the inauguration, with up to 700,000 expected to flood into the city for his address and the festivities surrounding it.

They filled street corners and stood in long snaking lines all around the Capitol and surrounding neighborhoods. Blocks from where Obama will be inaugurated, people shuffled down streets, snapping photos before sunrise. Many wore long coats, hats, scarfs, earmuffs and sequined Obama hats.

Bill Clinton and Jimmy Carter were in attendance, but former President H. W. Bush, released Monday from a Houston hospital and recuperating from bronchitis, was not attending. Neither was his son, former President George W. Bush.

The Obamas attended a service at 8:45 a.m. at St. John's Episcopal Church. It included prayers from Pastors Joel Hunter and Luis Leon, followed by a blessing by Bishop Vacti McKenzie. "Bless this administration with both favor and grace," McKenzie said. "Give them the resources and people necessary to get the job done"

First daughter Malia was in a playful mood as the family returned to the White House. As the president's limo pulled up, Malia sneaked up to surprise her dad, shouting "Boo!" as he got out. "You scared me!" he told her.

Around town, police and military authorities were part of a ubiquitous security presence, stretching from downtown to Metro train platforms in suburban Virginia and Maryland.

Coast Guard patrol boats were the only vessels plying the Potomac River. A large stretch of the river, from the Francis Scott Key Bridge to south of Ronald Reagan Washington National Airport, was closed to commercial and recreational users as part of an elaborate inaugural security plan.

Federal and local law enforcement officials reported no arrests throughout the morning. Crowd numbers, however, continued to run well behind the record 2009 inaugural.

Washington Metropolitan Area Transit Authority spokesman Dan Stessel said Monday that as of 11 a.m., 309,000 people had entered the metro train system, representing about 60% of 2009 numbers. "Second inaugurals are always lighter,'' Stessel said. "We saw that with the second Clinton, Bush and Reagan inaugurals.''

Stessel reported few problems, except for heavy crowding at the Federal Center Southwest station, a main destination for ticketed spectators at the swearing-in ceremony. "Overall, everything is running well,'' he said.

Dionne Davis, 36, of Columbus, Ohio, woke at 4 a.m. determined to get as close as she could to the festivities without an official ticket. She watched the last inauguration at home but decided this time she had to be here.

Davis traveled from a family member's home in Capitol Heights, Md., parked at the Metro and took a long train ride into the city. "I just want to be part of history," Davis said. "I want this to be something I can tell my kids and grandkids."

Briskly walking down 3rd Street at 6:30 a.m., Davis said she was happy to brush shoulders with other people. She's ready for a long day and has supplies to prove it.

"We ate before we left, I took my vitamins, and I got my bottle of water," she said. "I'm just excited. These are experiences that last forever."

"What the Inauguration reminds us of is the role we have as fellow citizens in promoting a common good even as we carry out our individual responsibilities," Obama told supporters during a reception Sunday. "The sense that there's something larger than ourselves that gives shape and meaning to our lives."

Obama begins his second term four years after inheriting an economic crisis and wars in Iraq and Afghanistan. The first Obama administration saw a national health care plan, a major stimulus bill, new financial regulations and an end to combat operations in Iraq, the winding down of the war in Afghanistan and the Navy SEAL raid that killed 9/11 mastermind Osama bin Laden in 2011.

Obama tangled with congressional Republicans who protested a record-setting rise of the federal debt, a slow-growing economy and a stubbornly high unemployment rate. Republicans still control the U.S. House.

As the president started a new term, throngs of well-wishers were in town.

Before 7 a.m., the Metro station closest to the Capitol building looked and sounded like a baseball stadium. Crowds flocked from trains and up the escalators, where they were greeted by vendors selling pins and posters while volunteers carrying "ask me" signs offered directions and greetings.

Vendors set up folding tables for several blocks along Pennsylvania Avenue behind the Capitol, selling trinkets ranging from Obama pins and T-shirts to knit caps embroidered "Obama: Back 2 Back"

"Good morning, welcome to the inauguration!" a pair of volunteers sang out to the crowd.

DuWanna Thomas, a lawyer and consultant from Atlanta, was on an Orange line Metro train headed to inauguration festivities by 6:15 a.m. She came to Obama's inauguration four years ago.

"This is very rewarding for me," said Thomas, armed with an Obama blanket and a small backpack with food. "It's just excellent. He's the best president."

Pam Johnson of Floyd, Iowa, was also on a Metro train by 6:15. She voted for President Obama twice and managed to snag a ticket to his second inauguration. "This is an experience of a lifetime for me to be right here, right now," said Johnson, president of the National Corn Growers Association. "When I found out the opportunity to go, I didn't want to miss it."

Johnson said she's especially excited to go to the Agriculture Ball tonight. "People call it the farm prom," she says.

Thomas Kannam, 8, came with his mom, dad and older sister. It's Kannam's first inauguration. "I want to see the president," Thomas said, holding tightly to a blanket wrapped around his shoulders for warmth.

The Kannam family from Durham, Conn., was on its way to a church prayer service before attending the inaugural parade. They got tickets through a friend who worked on Obama's campaign.

The New York African American Chamber of Commerce sent two buses with 56 people on each, according to Raquel Sanchez, 41, of New York. They arrived at around 5:45 a.m. Some were unable to put partisan politics aside.

"I hate the divide in the House and in Congress," said Stephanie Simmons, 59. Obama has struggled because Republicans won't work with him, Simmons said, which she said may be "a black-white thing" beyond regular partisan differences.